This invention relates to electrical installations. More particularly it relates to an electrical installation which includes pole- mounted electrical equipment, to a pole for such equipment, and to a method of earthing such equipment.

The conventional manner of earthing pole-mounted electrical equipment is to run a bare copper earthing conductor from an earth connection on the electrical equipment down the outside of one of the poles forming part of the support structure for the equipment, to an earthing point. Because of the value of copper, theft of earthing conductors has become a problem. This problem has become more acute as a result of a recently introduced requirement that earthing conductors should be insulated, and that the earthing arrangement should be such that no exposed part of the earthing conductor is nearer than 5 m to an exposed part of another earthing conductor. Insulated copper conductors are considerably more expensive than bare copper conductors.

Furthermore, in the case of new installations, the need to install the earthing conductor on site requires skilled personnel to spend time travelling to and from the site, adding to the cost of such installations.

Furthermore, the presence of earthing conductors running down the poles gives such installations an untidy appearance.

In is an object of the present invention to overcome or at least alleviate the above problems.

According to the invention there is provided an electrical installation which comprises a support structure including a wooden pole, electrical equipment mounted on the support structure, and an earthing conductor leading down the pole and through which

earthing conductor the electrical equipment is connected to an earthing point, the earthing conductor extending along a passage cut in the pole.

The passage may be in the form of a channel cut in the outer surface of the pole. The earthing conductor may be concealed by a cover strip which is accommodated in the channel.

The outer surface of the cover strip may be flush with the outer surface of the pole. The cover strip may be of wood.

The installation may further comprise a threaded bush at each opposite end of the earthing conductor, each threaded bush being set in the wooden pole and being connected to the earthing conductor, and electrical connection with the earthing conductor being established at each opposite end of the conductor by means of a threaded fastener which engages with the respective threaded bush.

The threaded bushes may be of stainless steel, and the earthing conductor may be of copper. The earthing conductor may be in the form of a stranded copper wire.

In an alternative form the earthing conductor may be of mild steel. It may be in the form of a flat mild steel bar. The threaded bushes may in this event also be of mild steel. The earthing conductor and the threaded bushes may be of galvanized mildsteel.

Further according to the invention there is provided a wooden pole for pole-mounted electrical equipment, the pole including an earthing conductor which extends along the pole and through which earthing conductor the electrical equipment can be connected to an earthing point, the earthing conductor extending along a passage cut in the pole.

Still further according to the invention there is provided, in an electrical installation which comprises a support structure

including a wooden pole and electrical equipment mounted on the support structure, a method of earthing the electrical equipment which comprises cutting a longitudinally extending passage in the pole, inserting an earthing conductor into the passage, and connecting an earth connection of the electrical equipment and an earthing point electrically to the earthing conductor.

The passage may be in the form of a channel which is cut in the outer surface of the pole by first securing a guide rail to the pole, so that the guide rail extends longitudinally of the pole, and then moving a cutting tool along the guide rail, whereby the channel is cut in the pole by the cutting tool.

The cutting tool may comprise a saw having a circular saw blade.

The guide rail may be removed again after the channel has been cut.

The invention will now be described in more detail, by way of example, with reference to the accompanying drawings.

In the drawings: Figure 1 is a side view of an electrical installation in accordance with the invention; Figure 2 is a detail section on ll-ll in Figure 1, showing a wooden pole and earthing means incorporated in the pole ; Figure 3 is an exploded view of the parts shown in Figure 2; Figure 4 is a broken plan view of the earthing means; Figure 5 is a view in the direction of arrow V in Figure 4; Figure 6 is a section on VI-VI in Figure 4, drawn to a larger scale, and showing also how the earthing means is secured to the pole and how a wire conductor is connected to the earthing means; Figure 7 is a cross-section illustrating a method of providing a pole with an earthing conductor in accordance with the invention; Figure 8 is a section similar to Figure 3, showing an alternative

arrangement in accordance with the invention; Figure 9 is a view similar to Figure 4, of the earthing means of Figure 8; Figure 10 is a view similar to Figure 5, of the earthing means of Figure 8; and Figure 11 is an exploded section on XI-XI in Figure 9, showing the earthing means and a wire conductor connected thereto.

Referring first to Figure 1, reference numeral 10 generally indicates an electrical installation in accordance with the invention, the installation comprising a support structure 12, electrical equipment in the form of a transformer 14 and a metering box 16 mounted on the support structure, and earthing means 18.1 and 18.2 through which the transformer and the metering box respectively are earthed.

The support structure 12 comprises wooden poles 20.1 and 20.2, the lower ends of which are set in footings below ground level, the ground level being indicated at 22.

Referring now also to Figures 2 to 6, the earthing means 18.1 is of hot-dipped galvanized mild steel and comprises an earthing conductor in the form of a flat bar 24, and a threaded bush 26 at each opposite end of the flat bar. The bushes 26 are welded to the flat bar. In a typical example the flat bar 24 may have a cross-section of 6 x 20mm, and each bush 26 may have a length of 40mm and an outside diameter of 30mm. In each bush 26 there is an axially extending, stepped hole. The wider part of the hole, which is indicated by reference numeral 28, is threaded, whereas the narrower part of the hole, which is indicated by reference numeral 30, is unthreaded.

To fit the earthing means 18.1 two holes 32 are drilled in the pole 20.1, one at a low level, and the other at a high level.

An 8mm wide channel 34 is then cut in the outer surface pole, the

channel extending from the one hole 32 to the other. The earthing means 18.1 is then set into the pole, with the threaded bushes 26 entering into the holes 32 and the flat bar 24 entering into the channel 34. The earthing means 18.1 is secured in position by means of a pair of brass screws, each of which is inserted into the hole of a respective one of the bushes 26 and engages with the shoulder between the wide and narrow parts of the hole. One of these screws is shown in dotted lines at 36 in Figure 6. A wooden cover strip 38 is then inserted into the channel 34 to cover the flat bar 24, the cover strip being secured in position by means of a suitable adhesive such as, for example, the adhesive that is available in the trade as"ABE 357", which is an epoxy-based adhesive. The outer surface of the cover strip 38 is preferably made flush with the outer surface of the pole 20.1.

The construction of the pole 20.2 and the earthing means 18.2 is similar, except that the flat bar 24 of the earthing means 18. 2 is shorter than that of the earthing means 18.1.

The transformer 14 has an earth connection 40 which is connected to the threaded bush 26 at the upper end of the earthing means 18.1, by means of a wire conductor 42. The wire conductor 42 has a lug 44 at each opposite end thereof. One of these lugs 44 is connected to the respective bush 26 by means of a threaded bolt 46 which engages with the threaded part 28 of the hole in the bush.

The bush 26 which is at the lower end of the earthing means 18.1, and which is below ground level 22, is connected electrically to an earthing spike 48 by means of an insulated wire conductor 50 which has a lug similar to the lug 44 at each opposite end thereof and is connected to the respective bush in a manner similar to that described above. The connection of the conductor 50 to the respective bush may be covered by an insulating compound such as that which is available in the trade as"SCOTCHFILL"putty.

The metering box 16 is mounted on steel cross bars 52 and may be earthed by virtue of one of the cross bars 52 being bolted directly to the upper bush 26 of the earthing means 18. 2.

The lower bush 26 of the earthing means 18.2 may be connected to an earthing spike 48 in a manner similar to that described above.

The poles 20.1 and 20.2 may be provided with the earthing means 18.1 and 18.2 respectively at a factory, before they are transported to the site for erection. In this event creosoting of the poles may take place after the conductors and the cover strips 38 have been put in place.

Existing, conventional support structures for supporting electrical equipment and comprising wooden poles can be modified in situ, to provide them with earthing means such as the earthing means 18.1 and 18.2 described above. In this event drilling of the lower one of holes 32 requires digging a hole in the ground next to the pole.

To facilitate cutting of the channel 34, a guide rail 54 as illustrated in Figure 7 may first be secured to the pole 20.1, the rail extending longitudinally of the pole. If desired, the rail 54 may be in a number of relatively short segments to facilitate transportation to and from the site. The rail 54 may be secured to the pole 20.1 by means of, for example, screws 56, brackets 58, and adjustable threaded rods 60. The rail 54 is of the type having a longitudinally extending guide formation 62. A cutting tool 64, in the form of a saw having a circular saw blade 66 is then moved along the rail 54, between the holes 32, thereby cutting the channel 34 in the pole.

The cutting tool has a formation 68 which co-operates with the guide formation 62, to guide the cutting tool along the rail 54. Once the channel 34 has been cut, the rail 54 can be removed again. The earthing means 18.1 and the cover strip 38 are then fitted as described above.

If desired, movement of the cutting tool 64 along the rail 54 may be mechanised by providing a hydraulic motor and a cable that runs on pulleys.

Referring now to Figures 8 to 11, reference numeral 18.3 indicates earthing means which comprises a pair of threaded bushes 70 of stainless steel, and a bare, stranded copper wire 72 connected to and extending between the two bushes. Each of the bushes 70 has a hole 74 transversely therethrough, for receiving the corresponding end of the copper wire 72. A grub screw 76 is provided to clamp the copper wire to the bush. The grub screw 76 has a hexagonal socket 78 therein, enabling the grub screw to be tightened by means of an Allen key.

The bushes 70 and the copper wire 72 are accommodated in sockets 32 and a slot 34 in the pole 20.1, as described above with reference to Figures 1 to 7. Likewise, as shown in Figure 11, a wire conductor 42 having a lug 44 at the end thereof can be connected to each of the bushes 70 by means of a bolt 46 which is screwed into the respective threaded bush.

This construction is advantageous as compared with the construction illustrated in Figures 2 to 6, in that it is easier to make up individual earthing means of different lengths for different poles, by simply cutting the copper wire 72 to the required length ; in that the bushes 70 do not need to be galvanized (galvanizing having the disadvantage that it tends to clog up the threads of the bush); and in that the copper wire is relatively flexible, which enables it better to accommodate poles which are somewhat warped.

Each of the bushes 70 is secured in position by means of a screw (not shown) that passes through a hole 80 in the bush, similar to the manner illustrated in Figure 6.